Many sewage and water treatment facilities in the past adopted the chlorine-ammonia treatment for disinfecting and destroying harmful micro-organisms in the water since the combination of chlorine and ammonia produced a more stable disinfecting residual than that produced by chlorine alone. The chlorine-ammonia treatment however, declined in popularity in the past several decades due to the emergence of "free residual" chlorination processes and to the superior bactericidal efficiency of hypochlorous acid. Currently, ammonia is being widely used as treatment for potable water effluents due to its ability to react with hypochlorous acid (formed when chlorine is added to water) to form chloramines which are not harmful or carcinogenic to humans in small amounts, and like hypochlorous acid, retains the oxidizing power of the chlorine.
Ammonia may be injected into water to be treated by ammoniators. The feeding of ammonia into water, particularly potable hard water, for example, having high concentrations of calcium, flowing under pressure in a pipe or water main, creates problems which are substantially overcome by the apparatus of the present invention.
More specifically, ammonia is highly soluble in water. During normal feeding of ammonia thereinto, the ammonia is readily absorbed by the water flowing past the ammonia discharge point. When the ammonia feed is discontinued, rapid absorption of the ammonia remaining in the feed lines causes the water to be drawn back thereinto with resultant flooding of the apparatus.
While backflows can ordinarily be prevented by a properly disposed check valve, another problem arises from the formation of calcium carbonate which precipitates from solution when ammonia is absorbed by hard water. Calcium carbonate is a hard insoluble scale material which will build up on any structure immersed in the water, thereby causing plugging and clogging of feed lines and failure or malfunctioning of the check valve. Frequent scale removal thus becomes necessary if proper equipment operation is to be maintained. Since components disposed or mounted within the feed pipe must be removed for descaling, any scale build-up in the feed pipe itself makes withdrawal of these components therefrom more difficult.
In the present invention, the ammonia injection tube is mounted vertically so that the ammonia is discharged downwardly into the water main. The improved check valve is mounted in a vertically disposed portion of an ammonia feed supply pipe well above the water main such that water does not frequently contact the check valve during normal operation, and hence scale build-up thereon is minimized. On shut-down, even though the ammonia in the feed lines dissolves in the water to draw it into the tube, the resultant ammonia-water solution is effectively isolated from the main water stream to further minimize scale formation on the valve. But regardless of the measures taken to prevent scale build-up on the valve and in the feed lines, some water will come in contact with the valve to form a scale thereon, notwithstanding the valve will preferably be made of polytetrafluoroethylene which discourages adhesion of scales thereon and optional air-purging of the the feed lines upon ammonia shut-down, later described.
The improved check valve of the present invention employs elastomeric O-rings, as do some other known check valves, for sealing off radial ports provided in the valve body when pressures therewithin are too low to sufficiently expand the O-rings from their sealing relationship. The valve body however is provided with an unique seating arrangement for the O-rings which positively prevents scale from forming on the valve at those portions thereof where descaling is considered necessary, regardless of the hardness of the water being treated. The unique seating arrangement also provides a more sensitive and faster responding valve, is easier to fabricate or mold since no tapered valve seats are required, and permits ammonia to be discharged from the valve in discrete form, such as bubbles, rather than in less discrete form, thus enabling a greater surface area of the ammonia to contact the water for more efficient treatment thereof.